import java.lang.Throwable;
import java.lang.Math;

public class Test1 {
    public static void main(String[] args) {

        try {
            showArea(1,2,3);
        } catch(TriangleException e) {
//            e.printStackTrace();
            System.out.println(e);
        }

    }

    public static void showArea(int a, int b, int c) throws TriangleException {
        double p = (a + b + c) / 2.0;

        double num = p * (p - a) * (p - b) * (p - c);

        if (num <= 0) {
            throw new TriangleException();
        }

        System.out.println(Math.sqrt(num));
    }
}

class TriangleException extends Exception {
    public TriangleException() {
        System.out.println("无法构成三角形");
    }
}